Novel arenavirus isolated from ticks in Florida

The mechanisms allowing viruses to break species barriers are crucial for risk assessment and control of emerging zoonotic pathogens. New World (NW) arenaviruses are a diverse family of rodent-borne zoonotic pathogens that include several causative agents of severe viral hemorrhagic fevers. The close genetic relationship of non-pathogenic and pathogenic NW arenaviruses is of considerable concern regarding spillover. The recent isolation of Tacaribe virus from Amblyomma americanum ticks in Florida provided first evidence for the presence of NW arenaviruses in arthropods. Considering the broad host range and complex ecology of host-seeking A. americanum ticks, we employed unbiased next generation sequencing to detect the presence of other arenaviruses. Our screen revealed genetic traces of the NW arenavirus Tamiami (TAMV) that was first isolated from the Florida cotton rat Sigmodon hispidus in 1965. The unique non-reciprocal superinfection capacity of TAMV allowed isolation of replicating virus by serial passaging, confirmed by sequencing and immunofluorescence. The nucleotide and amino acid sequences of the new tick-derived isolate TAMV-Florida (TAMV-FL) deviated significantly from known TAMV strains, excluding laboratory contaminations. The TAMV-FL acquired several mutations in the envelope glycoprotein (GP) that is a key determinant for receptor specificity and vial tropism. Combining molecular modelling with functional studies in a biocontained recombinant pseudotype system, we found that the acquired mutations lowered the viral fusion pH of TAMV-FL GP, allowing exit of the virus from later endosomal compartments. Examination of receptor specificity showed increased use of human receptor orthologues by TAMV-FL when compared to the original rodent-borne TAMV isolate, suggesting ongoing adaptation.